Islet autoantibodies, nationality and gender: a multinational screening study in first-degree relatives of patients with Type I diabetes

Aims/hypothesis. First-degree relatives of patients with Type I (insulin-dependent) diabetes mellitus diagnosed at 20 years of age or under were screened for islet cell antibodies (ICA) in the course of recruitment to an international diabetes prevention trial. Our aim was to evaluate the influence of age, gender, proband characteristics and nationality on the prevalence of ICA and co-existence of autoantibodies to GAD, IA-2 and insulin. Methods. A central laboratory screened samples from 10326 non-diabetic relatives who were aged less than 40 years, from eight European countries for ICA. Antibodies to GAD and IA-2 were measured in all samples with ICA of 10 JDF units or more. Results. Overall, 8.9 % of relatives had ICA of 10 JDF units or more, 3.8 % with ICA of 20 JDF units or more. Of 921 relatives with ICA of 10 JDF units or more, 29 % had co-existing antibodies to GAD or IA-2 or both. ICA of 10 JDF units or more were more prevalent in males (10.8 %) than females (7.3 %). ICA with GAD or IA-2 antibodies or both were also more common in males (3.4 %) than females (1.9 %) and in relatives under 20 years of age (3.5 % vs 1.5 %). Multiple regression analysis showed nationality to be a determinant of ICA of 10 JDF units or more but not of ICA of 20 JDF units or more or of ICA with co-existing islet antibodies, and confirmed the importance of age and gender as determinants of islet autoimmunity. Conclusions/interpretation. Relatives from different European countries have similar rates of islet autoimmunity despite wide variation in the background incidence of childhood diabetes, and male excess is equally evident in all populations. The male excess of ICA and islet autoimmunity over 10 years of age reflects the higher male incidence of Type I diabetes in this age group, and suggests that boys may be more likely than girls to develop islet autoimmunity during adolescence.